Polyphenylene ether resins are superior in their mechanical properties, electric properties, heat resistance, hydrolysis resistance and dimensional stability, and are extensively used as thermoplastic engineering plastic resins.
As a flame resisting polyphenylene ether resin composition, there is known a resin composition comprising a polyphenylene ether resin and a halogen-containing flame retardant or a phosphorus-containing flame retardant. Nowadays, however, a polyphenylene ether resin composition comprising neither any halogen-containing flame retardant nor any phosphorus-containing flame retardant is increasingly required, because of an anxiety such that such a flame retardant may affect the environment.
As a polyphenylene ether resin composition comprising neither the halogen-containing flame retardant nor the phosphorus-containing flame retardant and having an improved flame resistance, U.S. Pat. No. 5,169,887 discloses a composition comprising a polyphenylene ether resin and a liquid straight chain phenylsiloxane.
In addition, U.S. Pat. No. 5,294,655 discloses a composition having an improved flame resistance, which comprises a polyphenylene ether resin, a liquid straight chain phenylsiloxane and a block copolymer elastomer.
Each of the references referred to above is incorporated herein by reference in its entirety.
Although the compositions disclosed in the above U.S. Patents are superior in their flame resistance to the polyphenylene ether resin per se, its level is not satisfactory. Particularly, there is left a problem in that when the polyphenylene ether resin is used in combination with a polystyrene resin, the resulting polyphenylene ether resin composition is insufficient in its flame resistance.